The present invention concerns, first, a method of manufacturing a pressurized two-chambered container, especially a rotationally symmetrical aerosol can. The method comprises forming a housing with an opening that can be tightly sealed by a barrier, especially a spray-or-aerosol valve, and that the product can be released through, with a product chamber and a propellant chamber separated fluid-tight from each other by a flexible diaphragm in the housing, whereby the product chamber can be charged with product, the propellant chamber can be charged with a compressed propellant, and the product chamber communicates with the product-release opening. The present invention also concerns a device for carrying out the method.
Pressurized containers, aerosol cans for instance, are increasingly widely used for hair-care products, spray-on lacquers, automotive-maintenance sprays, furniture-care sprays, etc. The product is subjected to pressure by a propellant. When a product release, usually a valve, is actuated, the propellant forces the product out through it in the desired state, a jet. Pressurized containers comprising two chambers work similarly, with the product under pressure. Conventional aerosol cans comprise only one chamber, and can accidentally release propellant unmixed with product, which is why the can needs to be shaken before use. The propellant in a two-chambered pressurized container on the other hand is entirely separate from the product. There are considerable advantages. The product can be employed along with a propellant that is not compatible with it. The propellant is not released, which is highly desirable environmentally, and can even be recycled once the product has been used up.
Two-chambered pressurized containers wherein the propellant chamber is separated from the product chamber by a plastic piston or by inserting a flexible diaphragm in the form of a plastic pouch are known. There ia a considerable drawback to pistons, however. Even slight deformations or unevenness in the wall of the housing can impede or jam a piston and render the container useless. Furthermore, the inside cross-section of the housing must be precisely constant in form and dimension along the total stroke traveled by the piston, severely restricting the number of shapes that can be employed. Again, many aerosol cans have bulging tops, and some product is always left over inside, downstream of the piston""s face. In versions that employ a plastic pouch of whatever shape, the pouch is inserted into the can through the product-release opening during manufacture and can be damaged. In mass production, this procedure must be carried out as rapidly as possible, often perforating or severely deforming the pouch to the extent that the container cannot be used. Known pressurized two-chambered containers can accordingly be manufactured only at a relatively high rate of rejects and are accordingly not entirely profitable.
One object of the present invention is a method of manufacturing pressurized two-chambered containers of any desired shape that can be carried out more economically than known methods. Another object is a device for carrying out the method.
The first object is attained in accordance with the present invention in an improved method of the aforesaid genus characterized in that the flexible diaphragm is inserted into a blank through at least one end that has been left open therein, subsequent to which the blank is finally shaped into a pressurized two-chambered container housing.
The flexible diaphragm, meaning the plastic pouch or similar structure in particular, is accordingly inserted into the housing that will demarcate the pressurized two-chambered container through a still entirely wide-open end before the housing is finally formed. Only then is the end finally formed, entirely closed, that is, or narrowed into a product outlet for example. The flexible diaphragm can be inserted into the blank at a high rate (higher than 100 per minute) through the still-open end, with no risk of damage or deformation and, once inside, shaped into any desired conformation without detriment to its function. Even bulging aerosol cans with product releases that are very small in relation to the volume of product in the product chamber can accordingly be manufactured particularly profitably and with a low percentage of rejects in the form of mass-produced pressurized two-chambered containers.
The device for carrying out the method in accordance with the present invention includes a mechanism for presenting the housing blank, in particular a rotationally symmetrical aluminum blank still entirely open at at least one end, a mechanism for inserting the flexible and fluid-tight diaphragm into the blank through the still entirely open end, a mechanism for forming the housing along with its product-release opening out of the blank, especially by reforming the edge of the open end to narrow it into a mouthpiece that accommodates the product release, and a mechanism for fastening and sealing the edge of the diaphragm to the housing while keeping the product chamber, which communicates with the product release, separate from the propellant chamber.
The subsidiary claims address advantageous embodiments of the present invention.
In one preferred embodiment of the method, the end of the housing that will constitute the mouthpiece with its product release in the finished housing is left open. In most aerosol cans, spray cans for instance, this will be the upper end. In the present embodiment, this section is reformed into a mouthpiece without adding anything extra, a cap for instance, which can be applied later. Preferably, this edge can be reformed by the application of such procedures appropriate for narrowing the housing at that section as bending, upsetting, or rolling for instance. The edge of the product release is preferably beaded to prevent injury and damage from sharp edges. The most preferable material for the housing blank is aluminum. The diaphragm can be plastic, especially thermoplastic, a plastic laminate, or composite sheet, preferably of or including a thermoplastic, that can resist other thermoplastics. In one particularly preferred embodiment of the present invention, the end (usually the base) of the blank pointing away from the site of the product release is provided, before the diaphragm is inserted, with a port that the diaphragm can be manipulated through inside the blank. The diaphragm can accordingly be shifted around inside the blank while the product release is being processed with no need to introduce a tool or other object through the open end. The pressurized two-chambered container can also be subsequently charged with propellant through this port. The diaphragm can preferably be an at least partly thermoplastic pouch. The pouch can easily be secured and sealed to the housing by heating and fusion, the propellant chamber being separated from the product chamber. It is of course conceivable in principle to secure at least one edge of the diaphragm to one wall of the blank before the latter has been formed. The simplest and most efficient approach to manufacturing such a pressurized two-chambered container when a pouch is employed as a diaphragm, however, is to fasten and seal the edge of the pouch to the edge of the product release. The pouch and the product chamber it occupies will accordingly be entirely enclosed in the propellant chamber. The pouch in one preferred embodiment is protected from any heat that might be released as the mouthpiece is being reformed by only subsequently raising the edge of the pouch beyond the edge of the product-release opening and fastening it thereto. The edge of the pouch can be lifted through the port facing the product release by subjecting the pouch to compressed air with a pneumatic tool or to the mechanical force of a tappet. In still another preferred embodiment, heated tool points fasten the pouch first to one inner edge of the housing by pressure applied to various points or areas for example. The projecting edge of the accordingly preliminarily secured pouch is then preferably wrapped around the edge of the product-release opening and fastened fluid-tight thereto by a hot wrapping-and-fastening tool, which expands and advances toward the edge. This approach is of particular advantage in that the edge of thermoplastic pouch will shrink as it cools and nestle tight against the edge of the product-release opening. This process will ensure additional sealing and tightness.
The device preferably includes, first, a mechanism for raising a diaphragm in the form of a pouch, especially of thermoplastic, by subjecting it to compressed air or to a tappet through a port in the end of the housing opposite the product release until the edge of the pouch projects beyond the edge of the product-release opening, second, a head preferably including segments equally distributed around it that heat up, spread out, and seize the edge of the pouch, securing it preliminarily to an inner edge of the housing, and third, a mechanism that heats up, preferably spreads out, and wraps the preliminarily secured projecting edge over the edge of the product-release opening, fastening it there permanently and tight by plasticizing it.